1. Field of the Invention
The present disclosure relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a method of driving the same.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, many efforts and studies are being made to develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs), as a substitute for CRTs. Of these flat panel displays, LCD devices have many advantages, such as high resolution, light weight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field into the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
The LCD devices are categorized into TN (twisted nematic) mode LCD devices, VA (vertical alignment) mode LCD devices, and IPS (in-plane switching) mode LCD devices. Of theses LCD devices, the IPS mode LCD devices have an advantage of wide viewing angles. The IPS mode LCD device has a liquid crystal layer operated by an in-plane electric field.
FIG. 1 is a circuit diagram of a pixel of an LCD device according to the related art.
Referring to FIG. 1, the LCD device includes gate and data lines GL and DL crossing each other to define a pixel region. In the pixel region, a thin film transistor T connected to the gate and data lines GL and DL, and a storage capacitor Cst and a liquid crystal capacitor Clc connected to the thin film transistor T are formed. The liquid crystal capacitor Clc includes a pixel electrode, a common electrode and a liquid crystal layer therebetween. The pixel electrode is connected to a drain electrode of the thin film transistor T.
When a pixel voltage and a common voltage are applied to the pixel electrode and the common electrode, respectively, an electric field is induced between the pixel and common electrodes and operates the liquid crystal layer. The storage capacitor Cst functions to storage the pixel voltage.
FIG. 2 is a schematic view illustrating an LCD device according to the related art.
Referring to FIG. 2, the LCD device includes a plurality of gate lines GLn−1, GLn and GLn+1 and a plurality of data lines DLm−1, DLm and DLm+1 to define pixel regions arranged in a matrix form.
In the pixel region, a thin film transistor T connected to the corresponding gate and data lines and a storage capacitor Cst connected to the thin film transistor T are formed. An electrode of the storage capacitor Cst is connected to a drain electrode of the thin film transistor T, and another electrode of the storage capacitor Cst is connected to a common line.
The LCD device is operated in a line inversion method or a dot inversion method. To do this, a common voltage is inverted in polarity per frame in synchronization with a gate signal and applied to the corresponding common line.
FIG. 3A is a plan view illustrating an array substrate of an LCD device according to the related art, and FIG. 3B is a cross-sectional view taken along a line III-III of FIG. 3A.
Referring to FIGS. 3A and 3B, the array substrate includes gate and data lines 12 and 22 on a substrate 10 crossing each other to define a pixel region. A gate insulating layer 13 is between the gate and data lines 12 and 22. In the pixel region, a thin film transistor T connected to the gate and data lines 12 and 22 is formed. The thin film transistor includes a gate electrode 11, a semiconductor layer 15, and source and drain electrodes 17 and 19.
A pixel electrode 20 is formed in the pixel region P and connected to the drain electrode 19 of the thin film transistor T. The pixel electrode 20 is formed on the gate insulating layer 13, and spaced apart from the data line 22 to prevent a short circuit with the data line 22.
A passivation layer 24 is formed on the data line 22 and the pixel electrode 20. A common electrode 26 is formed on the passivation layer 24 corresponding to the pixel electrode 20 and includes a plurality of bar-shaped openings OA.
When a gate signal and a data signal are applied to the gate and data lines 12 and 22, respectively, the thin film transistor T is turned on according to the gate signal, and the data signal passes through the thin film transistor T and is applied to the pixel electrode 20 as a pixel voltage. When a common voltage is applied to the common electrode 26, an electric field induced by the pixel voltage and the common voltage operates a liquid crystal layer.
FIGS. 4A and 4B are views illustrating waveforms of pixel and common voltages in a line inversion method and a pixel inversion method, respectively, according to the related art.
Referring to FIG. 4A, in the line inversion method, a pixel voltage Vdata is inverted in polarity per line and per frame according to a polarity control signal that is generated from a timing control portion. A common voltage Vcom is inverted in polarity opposite to the pixel voltage Vdata.
For example, further referring to FIG. 2, a pixel region at a coordinate (n−1, m−1) is supplied with a data voltage Vdata of a positive polarity (+) while a pixel region at a coordinate (n, m−1) is supplied with a data voltage Vdata of a negative polarity (−). In this case, the pixel region at (n−1, m−1) is supplied with a common voltage Vcom of a negative polarity (−) while the pixel region at (n, m−1) is supplied with a common voltage Vcom of a positive polarity (+).
Referring to FIG. 4B, in the pixel inversion method, a common voltage Vcom is constant while a pixel voltage Vdata is inverted in polarity with respect to the common voltage Vcom.
In the related art LCD device operated in the above inversion methods, a common voltage supply portion is used to supply the common voltage to all pixel regions. In this case, since the common voltage is supplied to all pixel regions, power consumption increases.